1. Field of the Invention
This invention lies in the field of gas burners for burning waste, low-pressure, lean gas that has some combustible material. More particularly, it concerns the design of a burner which can utilize low calorific value gas alone, or in combination with rich gas, in a furnace, for the production of rich radiance from the burner to assist in ultimate heat transfer.
2. Description of the Prior Art
Demand for fuel conservation is an important consideration today, and makes the use of combustion air preheat by waste heat usage, for increased heat energy conservation, a greatly preferred practice through significantly increased efficiency of use of fuel-provided sensible heat.
In the prior art, premix operation of fuel and air makes it decidely a cumbersome and essentially impossible operation to substitute hot (preheated) air for the normally used cold air, for a number of reasons, which are well-known to those versed in the art of such gaseous fuel burning.
The prior art systems are typically used in chemical operations for processing raw materials, and it is typical for those process operations to produce waste gases which have useful calorific value, but which cannot be used in gas burners designed for limited fuel characteristics. As an example, the waste gas having calorific value of, say, 200 btu/cf LHV cannot be burned effectively in burners which have been designed for 910 btu/cf LHV methane or natural gas.
There is a great effort to make use of the waste gases, which are in ample supply, as process fuel, but this is not possible with conventional burners, for various reasons aside from lower calorific value. Because of this ordinarily there cannot be full usage of all available fuel, which results in energy waste. Waste gases having calorific value as low as 50 btu/cf are capable of heat energy production in a useful manner, if it is possible to burn them as fuel.
Such waste gases are generally produced only after particular processes become operational, and it is necessary to use a standard fuel, such as natural gas, for example, for heat production required to cause the process to become operational, or for start-up. It, therefore, is necessary for gas burners to be suitable for operation with either, or both, natural gas or the waste gas in typically-used premix gas burners. Since combustion air is supplied for the burner at pressure greater than atmospheric pressure, and gas energy is not required for inspiration of air for combustion, this becomes possible. The prior art burners make use of gas fuel energy as it is discharged from high (15 lb.) supply pressure into the atmosphere, in order to supply air for combustion, in typical self-inspirating atmospheric air pressure burners.
If the waste gases have calorific value because of the presence within them of combustible matter, other than free hydrogen, it is advantageous to premix a selected quantity of air with the fuel before the fuel-air mixture is discharged for burning. If free hydrogen is a predominant fuel combustible, such premix operation is undesirable and dangerous because of possible flashback of flame into the burner structure, which could severely damage the burner.